Blow molding grade HDPE is a certain type of HDPE. HDPE stands for High Density Polyethylene, and is produced in the same fashion as other forms of polyethylene, but in such a fashion as to ensure that the polyethylene molecule chains are long and densely packed, as opposed to being branching and not so densely packed. HDPE is differentiated from other forms of polyethylene simply by its molecular density, but there are also deviations within HDPE which make some types of HDPE suitable for certain manufacturing applications and not others.
Blow molding grade HDPE pellets are produced through an extrusion process, where melted blow molding grade HDPE is pressed through a steel plate with holes cut in it (known as a die), and a cutting blade at the end of it which slices the HDPE into the right length. Blow molding grade HDPE pellets are an excellent source of homogeneous blow molding grade HDPE, and are easily transported due to the density with which they can be packed.
How Are Blow Molding Grade HDPE Pellets Graded?
The grading system is mostly based on a measure known as the Melt Flow Index, or MFI. The MFI simply refers to how viscous the HDPE is when melted. Some forms of HDPE are very runny, and flow quickly. These forms have a high MFI. Other forms of HDPE are very thick when they are melted, and flow much more slowly. These forms of HDPE have a low MFI.
Blow Molding Grade HDPE is HDPE with a relatively low melt flow index. This means that when melted, the HDPE is fairly viscous, flows slowly, and is resistant to the forces of gravity. This makes it perfect for blow molding applications where HDPE is blown up into shape inside a mold through the forces of compressed air. It is essential that if one is undertaking blow molding applications, that one obtains a source of blow molding grade HDPE, as other grades of HDPE are likely to simply flow to the bottom of the mold and produce deformed or structurally flawed products.
Sources Of Blow Molding Grade HDPE Pellets
Blow molding grade HDPE pellets can be manufactured from virgin HDPE, or it can be produced from reprocessed HDPE. The source makes little difference when it comes to the melt flow index and the resulting grade of the HDPE. The source may make a considerable difference to the quality of the HDPE however. If you require a very clean and pure source of HDPE, to be used in toys or food packaging applications, for instance, then virgin blow molding grade HDPE is the better option. Virgin HDPE is the only form of HDPE allowed in food contact applications, and it also has the added advantage of being nice and translucent, which makes for nice translucent products, or if you would like to add color, very brightly colored products. Reprocessed HDPE is more suitable for the manufacturing of products that are hidden, or black products. It is also worth mentioning that reprocessed HDPE, whilst having been very carefully screened, cleaned and filtered, is still slightly contaminated and less strong than pure virgin HDPE. For many manufacturing applications, the slight deviances are immaterial however, and reprocessed blow molding grade HDPE pellets can be used with confidence.